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Wikipedia says its in 11/4, but I think it sounds more like a 12/8 with the last note skipped - aka 11/8.

Here's another quote from Wikipedia:
As Gregg Allman later said:
"I didn't know the intro was in 11/4 time. I just saw it as three sets of three, and then two to jump on the next three sets with: it was like 1,2,3—1,2,3—1,2,3—1,2. I didn't count it as 1,2,3,4,5,6,7,8,9,10,11. It was one beat short, but it didn't feel one short, because to get back to the triad, you had two steps to go up. You'd really hit those two hard, to accent them, so that would separate the threes. ... [Duane] said, 'That's good man, I didn't know that you understood 11/4.' Of course I said something intelligent like, 'What's 11/4?' Duane just said, 'Okay, dumbass, I'll try to draw it up on paper for you.'"[11]